Plastic materials can be used in a wide variety of packaging, wrapping, and storage articles. Plastic materials traditionally have not had good barrier properties to gases (particularly oxygen). Plastics have generally functioned poorly at excluding oxygen passage compared with other available materials, such as glass or metal. However, despite this shortcoming, some plastic materials have become widely used for some packaging applications. For example, polyethylene terephthalate (PET) has become widely used for soft drink bottles, water bottles, and the like. However, the barrier properties of PET have limited its use for other applications in which the package contents are more susceptible to degradation from exposure to oxygen. For example, glass still predominates in juice and beer bottling.
To reduce gas transmission of a plastic packaging material, a passive barrier may be used to hinder the passage of a gas, e.g. oxygen. For example, in a multi-layer bottle, the inner and outer layers may be made of PET, while the center layer is a different material with passive barrier properties such as, for example, ethylene vinyl alcohol (EVA). However, layers of dissimilar materials often do not adhere well to one another, and an adhesive between the layers may be required to prevent delamination. The clarity of the packaging material may be reduced when a passive barrier material is used, and the multi-layered material may be more difficult to recycle.
An active oxygen-scavenging system, which reduces or depletes the oxygen in an environment, may be used to overcome at least some of the limitations of a passive barrier system. An active oxygen scavenger, such as a polyamide or a polyolefin, may be incorporated into the backbone of a base polymer material making up the walls of the package to form an oxygen-scavenging polymer. The oxygen-scavenging polymer may be used in a blend with other polymers, or as an oxygen-scavenging layer in a multi-layer container. However, since the oxidation occurs in the backbone of the polymer, the properties of the oxygen-scavenging polymer may change compared to the unmodified base polymer. As a result of the oxidation, the polymer may even begin to degrade over time. Polyamide systems often yellow due to oxidation, and this oxidation may occur during injection molding of the original articles, during storage, use, or during recycling.
What is needed in the marketplace is an improved oxygen-scavenging polymer for use in articles such as packaging, wrapping and storage articles.